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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include "mongo/db/exec/sort_executor.h"
#include "mongo/db/index/sort_key_generator.h"
#include "mongo/db/pipeline/document_source.h"
#include "mongo/db/pipeline/document_source_limit.h"
#include "mongo/db/pipeline/expression.h"
#include "mongo/db/query/query_knobs_gen.h"
#include "mongo/db/query/sort_pattern.h"
#include "mongo/db/sorter/sorter.h"
namespace mongo {
class DocumentSourceSort final : public DocumentSource {
public:
static constexpr StringData kStageName = "$sort"_sd;
/**
* If there are any $limit stages that could be logically swapped forward to the position of the
* pipeline pointed to by 'itr' without changing the meaning of the query, removes these $limit
* stages from the Pipeline and returns the resulting limit. A single limit value is computed by
* taking the minimum after swapping each individual $limit stage forward.
*
* This method also implements the ability to swap a $limit before a $skip, by adding the value
* of the $skip to the value of the $limit.
*/
static boost::optional<long long> extractLimitForPushdown(
Pipeline::SourceContainer::iterator itr, Pipeline::SourceContainer* container);
const char* getSourceName() const final {
return kStageName.rawData();
}
void serializeToArray(
std::vector<Value>& array,
boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final;
GetModPathsReturn getModifiedPaths() const final {
// A $sort does not modify any paths.
return {GetModPathsReturn::Type::kFiniteSet, std::set<std::string>{}, {}};
}
StageConstraints constraints(Pipeline::SplitState) const final {
StageConstraints constraints(StreamType::kBlocking,
PositionRequirement::kNone,
HostTypeRequirement::kNone,
DiskUseRequirement::kWritesTmpData,
FacetRequirement::kAllowed,
TransactionRequirement::kAllowed,
LookupRequirement::kAllowed,
ChangeStreamRequirement::kBlacklist);
// Can't swap with a $match if a limit has been absorbed, as $match can't swap with $limit.
constraints.canSwapWithMatch = !_sortExecutor->hasLimit();
return constraints;
}
DepsTracker::State getDependencies(DepsTracker* deps) const final;
boost::optional<DistributedPlanLogic> distributedPlanLogic() final;
bool canRunInParallelBeforeWriteStage(
const std::set<std::string>& nameOfShardKeyFieldsUponEntryToStage) const final;
/**
* Returns the sort key pattern.
*/
const SortPattern& getSortKeyPattern() const {
return _sortExecutor->sortPattern();
}
/**
* Parses a $sort stage from the user-supplied BSON.
*/
static boost::intrusive_ptr<DocumentSource> createFromBson(
BSONElement elem, const boost::intrusive_ptr<ExpressionContext>& pExpCtx);
/**
* Convenience method for creating a $sort stage. If maxMemoryUsageBytes is boost::none,
* then it will actually use the value of internalQueryExecMaxBlockingSortBytes.
*/
static boost::intrusive_ptr<DocumentSourceSort> create(
const boost::intrusive_ptr<ExpressionContext>& pExpCtx,
BSONObj sortOrder,
uint64_t limit = 0,
boost::optional<uint64_t> maxMemoryUsageBytes = boost::none);
/**
* Returns the the limit, if a subsequent $limit stage has been coalesced with this $sort stage.
* Otherwise, returns boost::none.
*/
boost::optional<long long> getLimit() const;
/**
* Loads a document to be sorted. This can be used to sort a stream of documents that are not
* coming from another DocumentSource. Once all documents have been added, the caller must call
* loadingDone() before using getNext() to receive the documents in sorted order.
*/
void loadDocument(Document&& doc);
/**
* Signals to the sort stage that there will be no more input documents. It is an error to call
* loadDocument() once this method returns.
*/
void loadingDone();
/**
* Returns true if the sorter used disk while satisfying the query and false otherwise.
*/
bool usedDisk() final;
bool isPopulated() {
return _populated;
};
bool hasLimit() const {
return _sortExecutor->hasLimit();
}
protected:
GetNextResult doGetNext() final;
/**
* Attempts to absorb a subsequent $limit stage so that it can perform a top-k sort.
*/
Pipeline::SourceContainer::iterator doOptimizeAt(Pipeline::SourceContainer::iterator itr,
Pipeline::SourceContainer* container) final;
private:
DocumentSourceSort(const boost::intrusive_ptr<ExpressionContext>& pExpCtx,
const BSONObj& sortOrder,
uint64_t limit,
uint64_t maxMemoryUsageBytes);
Value serialize(boost::optional<ExplainOptions::Verbosity> explain = boost::none) const final {
MONGO_UNREACHABLE; // Should call serializeToArray instead.
}
/**
* Before returning anything, we have to consume all input and sort it. This method consumes all
* input and prepares the sorted stream '_output'.
*
* This method may not be able to finish populating the sorter in a single call if 'pSource'
* returns a DocumentSource::GetNextResult::kPauseExecution, so it returns the last
* GetNextResult encountered, which may be either kEOF or kPauseExecution.
*/
GetNextResult populate();
/**
* Returns the sort key for 'doc', as well as the document that should be entered into the
* sorter to eventually be returned. If we will need to later merge the sorted results with
* other results, this method adds the sort key as metadata onto 'doc' to speed up the merge
* later.
*/
std::pair<Value, Document> extractSortKey(Document&& doc) const;
bool _populated = false;
boost::optional<SortExecutor> _sortExecutor;
boost::optional<SortKeyGenerator> _sortKeyGen;
};
} // namespace mongo
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